Recently the technologies of the liquid crystal displays have been advanced and improved quickly. Moreover, the production cost of the liquid crystal displays is continuously reduced. Therefore, the traditional cathode ray tubes (CRT) are almost completely replaced by the liquid crystal displays (LCD) in the market of the monitors. As the technologies of LCD are being improved greatly, the market of LCD TV is growing fast, and the requirements and expectations for the performance of the LCD TV become higher and higher. Compared to the traditional CRT TV, the LCD TV has several advantages, such as much thinner dimension, lager screen size, much higher resolutions, etc. However, the LCD TC has its weakness, e.g. lower contrast ratio. Since the back light of the LCD TV is continuously turned on, nevertheless the light can hardly be blocked by the liquid crystal completely in the dark pictures due to the characteristics of the liquid crystal, and the resulted slight light leaking, for which the contrast ratio is reduced, occurs. Therefore the promotion of the contrast ratio becomes one of the important LCD techniques needed to be improved.
In order to promote the contrast ratio, as usual, the current technology instantly adjusts the brightness of the back light module according to the total luminance of the displayed picture. For example, when the total luminance of the picture to be displayed is low, the brightness of the back light module is instantly decreased; when the total luminance of the picture to be displayed is high, the brightness of the back light module is instantly increased. However, this method can easily cause the picture flickering and the displayed pictures to be suddenly darkening and lightening, which may make the audience uncomfortable and cause the vision fatigue. Meanwhile, the quickly and frequently adjusting the brightness of the back light module may reduce the lifetime of the back light module. On the other hand, though the reduction of the brightness of the back light module can increase the contrast ratio, the whole picture may look dim.
In order to solve the above-mentioned problems, the new concepts and the solutions are proposed in the present invention in order to promote the contrast ratio of the LCD and to effectively solve the problems of the picture flickering and the visual discomfort. The present invention is described below.